For road vehicles it is desirable to be able to distribute different drive torque to different wheels for improving the vehicle stability and/or performance. Torque vectoring units for road vehicles are thus known which purpose is to cause the drive torque distribution of a vehicle to change.
Such torque vectoring devices are arranged to shuffle drive torque laterally on a driven axle, or longitudinally between a driven axle and a non-driven axle.
In order to obtain the desired result with regard to the driving dynamics, it may in certain situations be advantageous to provide a drive wheel with a positive torque in relation to the other drive wheel on the driving axle. Such a positive torque may be obtained in a way known per se by a mechanical gear device for gearing-up or increasing the rotational speed of the drive shaft for the wheel in question by for example 10%.
Many examples of such mechanical gear devices are known. In such arrangements being both heavy and expensive, torque vectoring devices are arranged at either side of the central differential for the two drive shafts.
Hence, when a differential rotational speed between two wheels is requested the prior art devices are affecting the rotational speed relative the absolute rotational speed, leading to heavy devices having a relatively high power consumption.
In view of this, the applicant has previously presented a torque vectoring unit which overcomes the above mentioned drawbacks. Such unit, fully disclosed in WO2010101506, includes an electrical motor coupled to a driven axle of a road vehicle such that, upon activation, it provides a positive torque to one wheel and an opposite torque to another wheel, each wheels being disposed on the same axle.
The torque vectoring unit is arranged on a driven axle of the vehicle. The propulsion force may be provided by means of an electrical motor, such that the torque vectoring unit is operating on an electrical axle of the vehicle. Such electrical axles are highly attractive for providing four-wheeled drive in e.g. a hybrid car, i.e. a vehicle being equipped with a first transmission for providing propulsion torque to the front axle, and a second transmission for providing propulsion torque to the rear axle.
Although the previously presented unit is highly attractive, the increasing demands of the industry require improvements relating to performance, simplicity, space requirements, cost etc. Therefore, there is a need for an electrical axle with a torque vectoring unit, said electrical axle being more compact and more cost effective.